Findings

Seasonal adjustment

February 06, 2013

Abstract:How do we understand national climate change politics in the United States? Using a methodological innovation in network analysis, this paper analyzes discussions about the issue within the US Congress. Through this analysis, the ideological relationships among speakers providing Congressional testimony on the issue of climate change are mapped. For the first time, issue stances of actors are systematically aggregated in order to measure coalitions and consensus among political actors in American climate politics in a relational way. Our findings show how consensus formed around the economic implications of regulating greenhouse gases and the policy instrument that should do the regulating. The paper is separated into three sections. First, we review the ways scholars have looked at climate change policymaking in the United States, paying particular attention to those who have looked at the issue within the US Congress. Next, we present analysis of statements made during Congressional hearings on climate change over a four-year period. Our analysis demonstrates how a polarized ideological actor space in the 109th Congress transforms into a more consensual actor landscape in the 110th Congress, which is significantly less guided by partisan differences. This paper concludes by discussing how these findings help us understand shifting positions within American climate politics and the implications of these findings.

Abstract:From 1864 to 1972, the real price of oil fell by, on average, over one percent per year. This trend dramatically broke when prices for crude increased by over 650 percent from 1972 to 1980. Policy makers adopted several policies designed to keep oil prices in check and reduce consumption. Missing from these policies were taxes on either oil or gasoline, prompting a long economics literature documenting the inefficiencies of these alternative policies. In this paper, I review the policy discussion related to the transportation sector that occurred during the time through the lens of the printed press. In doing so, I pay particular attention to whether gasoline taxes were "on the table," as well as how consumers viewed the inefficient set of policies that were ultimately adopted. The discussions at the time suggest that meaningful changes in gasoline taxes were on the table; the public discussion seemed to be much greater than it is today. Some in Congress and many presidential advisors in the Nixon, Ford, and Carter administrations supported and proposed gasoline taxes. The main roadblocks for taxes were Congress and the American people. Polling evidence at the time suggests that consumers preferred price controls and rationing and vehicle taxes over higher gasoline taxes or letting gasoline prices clear the market. Given the saliency of rationing and vehicle taxes, it seems difficult to argue that these alternative polices were adopted because they hide their true costs.

Abstract:A series of polls provide new tests for how weather influences public beliefs about climate change. Statewide data from 5,000 random-sample telephone interviews conducted on 99 days over two and a half years (2010 to 2012) are merged with temperature and precipitation indicators derived from USHCN station records. The surveys carry a question designed around scientific consensus statements that climate change is happening now, caused mainly by human activities. Alternatively, respondents can state that climate change is not happening, or that it is happening but mainly for natural reasons. Belief that humans are changing the climate is predicted by temperature anomalies on the interview and previous day, controlling for season, survey and individual characteristics. Temperature effects concentrate among one subgroup, however: individuals who identify themselves as Independent, rather than aligned with a political party. Interviewed on unseasonably warm days, Independents tend to agree with the scientific consensus regarding anthropogenic climate change. On unseasonably cool days, they tend not to. Although temperature effects are sharpest for just a 2-day window, we see positive effects for longer windows as well. As future climate change shifts the distribution of anomalies and extremes, this will first affect beliefs among unaligned voters.

Gavin Foster & Eelco RohlingProceedings of the National Academy of Sciences, 22 January 2013, Pages 1209-1214

Abstract:On 103- to 106-year timescales, global sea level is determined largely by the volume of ice stored on land, which in turn largely reflects the thermal state of the Earth system. Here we use observations from five well-studied time slices covering the last 40 My to identify a well-defined and clearly sigmoidal relationship between atmospheric CO2 and sea level on geological (near-equilibrium) timescales. This strongly supports the dominant role of CO2 in determining Earth's climate on these timescales and suggests that other variables that influence long-term global climate (e.g., topography, ocean circulation) play a secondary role. The relationship between CO2 and sea level we describe portrays the "likely" (68% probability) long-term sea-level response after Earth system adjustment over many centuries. Because it appears largely independent of other boundary condition changes, it also may provide useful long-range predictions of future sea level. For instance, with CO2 stabilized at 400-450 ppm (as required for the frequently quoted "acceptable warming" of 2 °C), or even at AD 2011 levels of 392 ppm, we infer a likely (68% confidence) long-term sea-level rise of more than 9 m above the present. Therefore, our results imply that to avoid significantly elevated sea level in the long term, atmospheric CO2 should be reduced to levels similar to those of preindustrial times.

Abstract:This article describes a study employing a risk-assessment methodology for evaluating uncertain future climatic conditions. To understand the implications of uncertainty on risk and to provide a near-term rationale for policy interventions, the study estimated the impacts from responses to climate change on U.S. state- and national-level economic activity. The study used results of the climate-model CMIP3 dataset developed for the Intergovernmental Panel on Climate Change's (IPCC) Fourth Assessment Report to 1) estimate a proxy for representing climate uncertainty over the next 40 years, 2) map the simulated weather from the climate models hydrologically to the county level to determine the physical consequences on economic activity at the state level, and 3) perform a detailed, economy-wide, 70-industry analysis of economic impacts among the interdependent lower-48 states for the years 2010 through 2050. The analysis determined the interacting industry-level effects, employment impacts at the state level, interstate population migration, consequences to personal income, and ramifications for the U.S. trade balance. When compared to a baseline economic forecast, the calculations produced an average risk of damage of $1 trillion to the U.S. economy from climate change over the next 40 years, with losses in employment equivalent to nearly 7 million full-time jobs. Added uncertainty would increase the estimated risk.

Abstract:The 2012-13 influenza season had an unusually early and severe start in the US, succeeding the record mild 2011-12 influenza season, which occurred during the fourth warmest winter on record. Our analysis of climate and past US influenza epidemic seasons between 1997-98 to present indicates that warm winters tend to be followed by severe epidemics with early onset, and that these patterns are seen for both influenza A and B. We posit that fewer people are infected with influenza during warm winters, thereby leaving an unnaturally large fraction of susceptible individuals in the population going into the next season, which can lead to early and severe epidemics. In the event of continued global warming, warm winters such as that of 2011-12 are expected to occur more frequently. Our results thus suggest that expedited manufacture and distribution of influenza vaccines after mild winters has the potential to mitigate the severity of future influenza epidemics.

Abstract:As a result of global warming, precipitation is likely to increase in high latitudes and the tropics and to decrease in already dry subtropical regions. The absolute magnitude and regional details of such changes, however, remain intensely debated. As is well known from El Niño studies, sea-surface-temperature gradients across the tropical Pacific Ocean can strongly influence global rainfall. Palaeoproxy evidence indicates that the difference between the warm west Pacific and the colder east Pacific increased in past periods when the Earth warmed as a result of increased solar radiation. In contrast, in most model projections of future greenhouse warming this gradient weakens. It has not been clear how to reconcile these two findings. Here we show in climate model simulations that the tropical Pacific sea-surface-temperature gradient increases when the warming is due to increased solar radiation and decreases when it is due to increased greenhouse-gas forcing. For the same global surface temperature increase the latter pattern produces less rainfall, notably over tropical land, which explains why in the model the late twentieth century is warmer than in the Medieval Warm Period (around AD 1000-1250) but precipitation is less. This difference is consistent with the global tropospheric energy budget, which requires a balance between the latent heat released in precipitation and radiative cooling. The tropospheric cooling is less for increased greenhouse gases, which add radiative absorbers to the troposphere, than for increased solar heating, which is concentrated at the Earth's surface. Thus warming due to increased greenhouse gases produces a climate signature different from that of warming due to solar radiation changes.

Abstract:Mass coral bleaching events have become a widespread phenomenon causing serious concerns with regard to the survival of corals. Triggered by high ocean temperatures, bleaching events are projected to increase in frequency and intensity. Here, we provide a comprehensive global study of coral bleaching in terms of global mean temperature change, based on an extended set of emissions scenarios and models. We show that preserving >10% of coral reefs worldwide would require limiting warming to below 1.5 °C (atmosphere-ocean general circulation models (AOGCMs) range: 1.3-1.8 °C) relative to pre-industrial levels. Even under optimistic assumptions regarding corals' thermal adaptation, one-third (9-60%, 68% uncertainty range) of the world's coral reefs are projected to be subject to long-term degradation under the most optimistic new IPCC emissions scenario, RCP3-PD. Under RCP4.5 this fraction increases to two-thirds (30-88%, 68% uncertainty range). Possible effects of ocean acidification reducing thermal tolerance are assessed within a sensitivity experiment.

Abstract:There is great uncertainty about the impact of anthropogenic carbon on future economic wellbeing. We use DSICE, a DSGE extension of the DICE2007 model of William Nordhaus, which incorporates beliefs about the uncertain economic impact of possible climate tipping events and uses empirically plausible parameterizations of Epstein-Zin preferences to represent attitudes towards risk. We find that the uncertainty associated with anthropogenic climate change imply carbon taxes much higher than implied by deterministic models. This analysis indicates that the absence of uncertainty in DICE2007 and similar models may result in substantial understatement of the potential benefits of policies to reduce GHG emissions.

Abstract:Growth in biofuel production, which is meant to reduce greenhouse gas (GHG) emissions and fossil energy demand, is increasingly seen as a threat to food supply and natural habitats. Using photovoltaics (PV) to directly convert solar radiation into electricity for battery electric vehicles (BEVs) is an alternative to photosynthesis, which suffers from a very low energy conversion efficiency. Assessments need to be spatially explicit, since solar insolation and crop yields vary widely between locations. This paper therefore compares direct land use, life cycle GHG emissions and fossil fuel requirements of five different sun-to-wheels conversion pathways for every county in the contiguous U.S.: Ethanol from corn or switchgrass for internal combustion vehicles (ICVs), electricity from corn or switchgrass for BEVs, and PV electricity for BEVs. Even the most land-use efficient biomass-based pathway (i.e., switchgrass bioelectricity in U.S. counties with hypothetical crop yields of over 24 tonnes/ha) requires 29 times more land than the PV-based alternative in the same locations. PV BEV systems also have the lowest life cycle GHG emissions throughout the U.S. and the lowest fossil fuel inputs, except for locations with hypothetical switchgrass yields of 16 or more tonnes/ha. Including indirect land use effects further strengthens the case for PV.

Abstract:Legislation on biofuels production in the USA and Europe is directing food crops towards the production of grain-based ethanol, which can have detrimental consequences for soil carbon sequestration, nitrous oxide emissions, nitrate pollution, biodiversity and human health. An alternative is to grow lignocellulosic (cellulosic) crops on ‘marginal' lands. Cellulosic feedstocks can have positive environmental outcomes and could make up a substantial proportion of future energy portfolios. However, the availability of marginal lands for cellulosic feedstock production, and the resulting greenhouse gas (GHG) emissions, remains uncertain. Here we evaluate the potential for marginal lands in ten Midwestern US states to produce sizeable amounts of biomass and concurrently mitigate GHG emissions. In a comparative assessment of six alternative cropping systems over 20 years, we found that successional herbaceous vegetation, once well established, has a direct GHG emissions mitigation capacity that rivals that of purpose-grown crops (-851 ± 46 grams of CO2 equivalent emissions per square metre per year (gCO2e m-2 yr-1)). If fertilized, these communities have the capacity to produce about 63 ± 5 gigajoules of ethanol energy per hectare per year. By contrast, an adjacent, no-till corn-soybean-wheat rotation produces on average 41 ± 1 gigajoules of biofuel energy per hectare per year and has a net direct mitigation capacity of -397 ± 32 gCO2e m-2 yr-1; a continuous corn rotation would probably produce about 62 ± 7 gigajoules of biofuel energy per hectare per year, with 13% less mitigation. We also perform quantitative modelling of successional vegetation on marginal lands in the region at a resolution of 0.4 hectares, constrained by the requirement that each modelled location be within 80 kilometres of a potential biorefinery. Our results suggest that such vegetation could produce about 21 gigalitres of ethanol per year from around 11 million hectares, or approximately 25 per cent of the 2022 target for cellulosic biofuel mandated by the US Energy Independence and Security Act of 2007, with no initial carbon debt nor the indirect land-use costs associated with food-based biofuels. Other regional-scale aspects of biofuel sustainability, such as water quality and biodiversity, await future study.

Abstract:Black carbon aerosol plays a unique and important role in Earth's climate system. Black carbon is a type of carbonaceous material with a unique combination of physical properties. This assessment provides an evaluation of black-carbon climate forcing that is comprehensive in its inclusion of all known and relevant processes and that is quantitative in providing best estimates and uncertainties of the main forcing terms: direct solar absorption, influence on liquid, mixed-phase, and ice clouds, and deposition on snow and ice. These effects are calculated with climate models, but when possible, they are evaluated with both microphysical measurements and field observations. Predominant sources are combustion related; namely, fossil fuels for transportation, solid fuels for industrial and residential uses, and open burning of biomass. Total global emissions of black carbon using bottom-up inventory methods are 7500 Gg yr-1 in the year 2000 with an uncertainty range of 2000 to 29000. However, global atmospheric absorption attributable to black carbon is too low in many models, and should be increased by a factor of almost three. After this scaling, the best estimate for the industrial-era (1750 to 2005) direct radiative forcing of atmospheric black carbon is +0.71 W m-2 with 90% uncertainty bounds of (+0.08, +1.27) W m-2. Total direct forcing by all black carbon sources, without subtracting the pre-industrial background, is estimated as +0.88 (+0.17, +1.48) W m-2. Direct radiative forcing alone does not capture important rapid adjustment mechanisms. A framework is described and used for quantifying climate forcings, including rapid adjustments. The best estimate of industrial-era climate forcing of black carbon through all forcing mechanisms, including clouds and cryosphere forcing, is +1.1 W m-2 with 90% uncertainty bounds of +0.17 to +2.1 W m-2. Thus, there is a very high probability that black carbon emissions, independent of co-emitted species, have a positive forcing and warm the climate. We estimate that black carbon, with a total climate forcing of +1.1 W m-2, is the second most important human emission in terms of its climate-forcing in the present-day atmosphere; only carbon dioxide is estimated to have a greater forcing. Sources that emit black carbon also emit other short-lived species that may either cool or warm climate. Climate forcings from co-emitted species are estimated and used in the framework described herein. When the principal effects of co-emissions, including cooling agents such as sulfur dioxide, are included in net forcing, energy-related sources (fossil-fuel and biofuel) have an industrial-era climate forcing of +0.22 (-0.50 to +1.08) W m-2 during the first year after emission. For a few of these sources, such as diesel engines and possibly residential biofuels, warming is strong enough that eliminating all emissions from these sources would reduce net climate forcing (i.e., produce cooling). When open burning emissions, which emit high levels of organic matter, are included in the total, the best estimate of net industrial-era climate forcing by all black-carbon-rich sources becomes slightly negative (-0.06 W m-2 with 90% uncertainty bounds of -1.45 to +1.29 W m-2). The uncertainties in net climate forcing from black-carbon-rich sources are substantial, largely due to lack of knowledge about cloud interactions with both black carbon and co-emitted organic carbon. In prioritizing potential black-carbon mitigation actions, non-science factors, such as technical feasibility, costs, policy design, and implementation feasibility play important roles. The major sources of black carbon are presently in different stages with regard to the feasibility for near-term mitigation. This assessment, by evaluating the large number and complexity of the associated physical and radiative processes in black-carbon climate forcing, sets a baseline from which to improve future climate forcing estimates.

Abstract:The worldwide energy consumption in 2006 was close to 498 exajoules. This is equivalent to an energy convergence of 15.8 TW into the populated regions, where energy is consumed and dissipated into the atmosphere as heat. Although energy consumption is sparsely distributed over the vast Earth surface and is only about 0.3% of the total energy transport to the extratropics by atmospheric and oceanic circulations, this anthropogenic heating could disrupt the normal atmospheric circulation pattern and produce a far-reaching effect on surface air temperature. We identify the plausible climate impacts of energy consumption using a global climate model. The results show that the inclusion of energy use at 86 model grid points where it exceeds 0.4 W m-2 can lead to remote surface temperature changes by as much as 1 K in mid- and high latitudes in winter and autumn over North America and Eurasia. These regions correspond well to areas with large differences in surface temperature trends between observations and global warming simulations forced by all natural and anthropogenic forcings. We conclude that energy consumption is probably a missing forcing for the additional winter warming trends in observations.

Abstract:Technology transfer plays a key role in global efforts to reduce greenhouse gas emissions. In this paper, we characterize the factors that promote or hinder the international diffusion of climate-friendly technologies using detailed patent data from 96 countries for the period 1995-2007. The data provide strong evidence that lax Intellectual Property regimes have a strong and negative impact on the international diffusion of patented knowledge. Restrictions on international trade and foreign direct investment also hinder the diffusion of climate-friendly technologies. Surprisingly, local technological capabilities tend to discourage transfers. While broad indicators of technology capabilities are expected to facilitate transfers, this latter result stems from our technology-specific definition of local capabilities, which makes it possible to capture a substitution effect between local and foreign inventions.

Ikuko Kitaba et al.Proceedings of the National Academy of Sciences, 22 January 2013, Pages 1215-1220

Abstract:The climatic effects of cloud formation induced by galactic cosmic rays (CRs) has recently become a topic of much discussion. The CR-cloud connection suggests that variations in geomagnetic field intensity could change climate through modulation of CR flux. This hypothesis, however, is not well-tested using robust geological evidence. Here we present paleoclimate and paleoenvironment records of five interglacial periods that include two geomagnetic polarity reversals. Marine oxygen isotope stages 19 and 31 contain both anomalous cooling intervals during the sea-level highstands and the Matuyama-Brunhes and Lower Jaramillo reversals, respectively. This contrasts strongly with the typical interglacial climate that has the temperature maximum at the sea-level peak. The cooling occurred when the field intensity dropped to <40% of its present value, for which we estimate >40% increase in CR flux. The climate warmed rapidly when field intensity recovered. We suggest that geomagnetic field intensity can influence global climate through the modulation of CR flux.

Abstract:Characterizing climatological and hydrological responses to agricultural irrigation continues to be an important challenge to understanding the full impact of water management on the Earth's environment and hydrological cycle. In this study, we use a global climate model, combined with realistic estimates of regional agricultural water use, to simulate the local and remote impacts of irrigation in California's Central Valley. We demonstrate a clear mechanism that the resulting increase in evapotranspiration and water vapor export significantly impacts the atmospheric circulation in the southwestern United States, including strengthening the regional hydrological cycle. We also identify that irrigation in the Central Valley initiates a previously unknown, anthropogenic loop in the regional hydrological cycle, in which summer precipitation is increased by 15%, causing a corresponding increase in Colorado River streamflow of ~30%. Ultimately, some of this additional streamflow is returned to California via managed diversions through the Colorado River aqueduct and the All-American Canal.

Abstract:Impacts of climate change such as the effects on human discomfort, morbidity and mortality often depend on multiple climate variables. Thus, a comprehensive impact assessment is challenging and uncertainties in all contributing variables need to be taken into account. Here we show that uncertainties in some impact-relevant metrics such as extremes of health indicators are substantially smaller than generally anticipated. Models that project greater warming also show a stronger reduction in relative humidity. This joint behaviour of uncertainties is particularly pronounced in mid-continental land regions of the subtropics and mid-latitudes where the greatest changes in heat extremes are expected. The uncertainties in health-related metrics combining temperature and humidity are much smaller than if uncertainties in the two variables were independent. Such relationships also exist under present-day conditions where the effect of model biases in temperature and relative humidity largely cancel for combined quantities. Our results are consistent with thermodynamic first principles. More generally, the findings reveal a large potential for joint assessment of projection uncertainties in different variables used in impact studies.

Abstract:The last decade has produced record-breaking heat waves in many parts of the world. At the same time, it was globally the warmest since sufficient measurements started in the 19th century. Here we show that, worldwide, the number of local record-breaking monthly temperature extremes is now on average five times larger than expected in a climate with no long-term warming. This implies that on average there is an 80 % chance that a new monthly heat record is due to climatic change. Large regional differences exist in the number of observed records. Summertime records, which are associated with prolonged heat waves, increased by more than a factor of ten in some continental regions including parts of Europe, Africa, southern Asia and Amazonia. Overall, these high record numbers are quantitatively consistent with those expected for the observed climatic warming trend with added stationary white noise. In addition, we find that the observed records cluster both in space and in time. Strong El Niño years see additional records superimposed on the expected long-term rise. Under a medium global warming scenario, by the 2040s we predict the number of monthly heat records globally to be more than 12 times as high as in a climate with no long-term warming.

Abstract:Flowering times are well-documented indicators of the ecological effects of climate change and are linked to numerous ecosystem processes and trophic interactions. Dozens of studies have shown that flowering times for many spring-flowering plants have become earlier as a result of recent climate change, but it is uncertain if flowering times will continue to advance as temperatures rise. Here, we used long-term flowering records initiated by Henry David Thoreau in 1852 and Aldo Leopold in 1935 to investigate this question. Our analyses demonstrate that record-breaking spring temperatures in 2010 and 2012 in Massachusetts, USA, and 2012 in Wisconsin, USA, resulted in the earliest flowering times in recorded history for dozens of spring-flowering plants of the eastern United States. These dramatic advances in spring flowering were successfully predicted by historical relationships between flowering and spring temperature spanning up to 161 years of ecological change. These results demonstrate that numerous temperate plant species have yet to show obvious signs of physiological constraints on phenological advancement in the face of climate change.

Abstract:A major gap in predictive capability concerning the future evolution of the ice sheets was identified in the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change. As a consequence, it has been suggested that the AR4 estimates of future sea-level rise from this source may have been underestimated. Various approaches for addressing this problem have been tried, including semi-empirical models and conceptual studies. Here, we report a formalized pooling of expert views on uncertainties in future ice-sheet contributions using a structured elicitation approach. We find that the median estimate of such contributions is 29 cm - substantially larger than in the AR4 - while the upper 95th percentile value is 84 cm, implying a conceivable risk of a sea-level rise of greater than a metre by 2100. On the critical question of whether recent ice-sheet behaviour is due to variability in the ice sheet-climate system or reflects a long-term trend, expert opinion is shown to be both very uncertain and undecided.

Abstract:Observing the full range of climate change impacts at the local scale is difficult. Predicted rates of change are often small relative to interannual variability, and few locations have sufficiently comprehensive long-term records of environmental variables to enable researchers to observe the fine-scale patterns that may be important to understanding the influence of climate change on biological systems at the taxon, community, and ecosystem levels. We examined a 50-year meteorological and hydrological record from the Hubbard Brook Experimental Forest (HBEF) in New Hampshire, an intensively monitored Long-Term Ecological Research site. Of the examined climate metrics, trends in temperature were the most significant (ranging from 0.7 to 1.3 °C increase over 40-50 year records at 4 temperature stations), while analysis of precipitation and hydrologic data yielded mixed results. Regional records show generally similar trends over the same time period, though longer-term (70-102 year) trends are less dramatic. Taken together, the results from HBEF and the regional records indicate that the climate has warmed detectably over 50 years, with important consequences for hydrological processes. Understanding effects on ecosystems will require a diversity of metrics and concurrent ecological observations at a range of sites, as well as a recognition that ecosystems have existed in a directionally changing climate for decades, and are not necessarily in equilibrium with the current climate.

Abstract:Urban density both facilitates consumption opportunities and encourages individuals to drive less and walk and use public transit more. Using several data sets, we document that high quality of life consumer center cities are low carbon cities. We discuss possible causal channels for this association.

Abstract:The Gold Coast, Australia is a coastal resort city whose urban environment has evolved through a series of human interventions on the natural shoreline. Such cities rely on a perceived high quality environment which in turn is reliant on continuing maintenance (e.g. beach nourishment, inlet dredging, drainage). Climate change consequently holds particular challenges for coastal resort cities. Sea-level rise impacts are likely to be manifest in increased frequency of flooding and beach erosion episodes. Here we consider adaptation options for the city under various future sea-level rise (SLR) scenarios at the high end of current predictions for the next century (+1 m, +2 m and +5 m) with the proviso that the beach and waterways must be preserved to enable the city to continue to exist as a resort. We conclude that pre-planned adaptation would probably enable the city to survive SLR of 1 m. An unplanned response to the same SLR would likely be characterised by periodic crises, growing uncertainty and public unease and would have marginal chances of success. For a 2 m SLR we contend that even with an adaptation plan in place, the scale of measures required would severely stretch the city's resources. Under a 5 m SLR over the next century we do not believe that any amount of planning would enable the city to survive as a coastal resort. Any adaptation to SLR would involve increased cost to maintain the artificial coastal environment. Adaptation options are particularly constrained by the widespread development around the waterways of the back-barrier area. Unlike other coastal cities, resorts depend on a public perception of a high quality environment. Maintaining this perception under SLR imposes particular adaptation constraints on resort cities.

Abstract:For more than a decade, the target of keeping global warming below 2 °C has been a key focus of the international climate debate. In response, the scientific community has published a number of scenario studies that estimate the costs of achieving such a target. Producing these estimates remains a challenge, particularly because of relatively well known, but poorly quantified, uncertainties, and owing to limited integration of scientific knowledge across disciplines. The integrated assessment community, on the one hand, has extensively assessed the influence of technological and socio-economic uncertainties on low-carbon scenarios and associated costs. The climate modelling community, on the other hand, has spent years improving its understanding of the geophysical response of the Earth system to emissions of greenhouse gases. This geophysical response remains a key uncertainty in the cost of mitigation scenarios but has been integrated with assessments of other uncertainties in only a rudimentary manner, that is, for equilibrium conditions. Here we bridge this gap between the two research communities by generating distributions of the costs associated with limiting transient global temperature increase to below specific values, taking into account uncertainties in four factors: geophysical, technological, social and political. We find that political choices that delay mitigation have the largest effect on the cost-risk distribution, followed by geophysical uncertainties, social factors influencing future energy demand and, lastly, technological uncertainties surrounding the availability of greenhouse gas mitigation options. Our information on temperature risk and mitigation costs provides crucial information for policy-making, because it clarifies the relative importance of mitigation costs, energy demand and the timing of global action in reducing the risk of exceeding a global temperature increase of 2 °C, or other limits such as 3 °C or 1.5 °C, across a wide range of scenarios.

Abstract:This study investigates the presence of trends in annual maximum daily precipitation timeseries obtained from a global dataset of 8326 high quality land-based observing stations with more than 30 years of record over the period from 1900 to 2009. Two complementary statistical techniques were adopted to evaluate the possible non-stationary behaviour of this precipitation data. The first was a Mann-Kendall non-parametric trend test, and was used to evaluate the existence of monotonic trends. The second was a non-stationary generalised extreme value analysis, and was used to determine the strength of association between the precipitation extremes and globally averaged near-surface temperature. The outcomes are that statistically significant increasing trends can be detected at the global scale, with close to two-thirds of stations showing increases. Furthermore, there is a statistically significant association with globally averaged near-surface temperature, with the median intensity of extreme precipitation changing in proportion with changes in global mean temperature at a rate of between 5.9% and 7.7% per degree, depending on the method of analysis. This ratio was robust irrespective of record length or time period considered, and was not strongly biased by the uneven global coverage of precipitation data. Finally, there is a distinct meridional variation, with the greatest sensitivity occurring in the tropics and higher latitudes, and minima around 13°S and 11°N. The greatest uncertainty was near the equator due to the limited number of sufficiently long precipitation records, and there remains an urgent need to improve data collection in this region to better constrain future changes in tropical precipitation.

Abstract:The Middle East and North Africa (MENA) region can be considered as the most water-scarce region of the world. The Intergovernmental Panel on Climate Change projects strong changes in climate across MENA, further exacerbating pressure on available water resources. The objective of this study is to undertake a climate change assessment for 22 MENA countries in order to quantify the problems these countries may encounter up to 2050. To evaluate climate change in MENA, nine global circulation models representing two future periods (2020-2030 and 2040-2050) were statistically downscaled and compared with a current climate, defined as the period 2000-2009. Besides precipitation only this study also focuses on change in water demand by vegetation reference evapotranspiration (ETref). It was found that for both future periods the annual precipitation sum will decrease for the majority of countries, with decreases of 15-20% for the latter period. For some countries, e.g. Djibouti and Yemen, an increase in annual precipitation of 15-20% was found. The annual ETref shows an increase for all countries for both future periods, with the strongest increases for the latter period. For the extreme situation, it was found that the minimum monthly and annual precipitation sum does not become smaller in the future climate. It in fact increases. In contrast, the maximum monthly and annual ETref increases for all countries. This indicates that projected changes in demand are likely to have a more adverse effect than changes in supply. Spatial analysis showed that the largest precipitation decreases are to be found in southern Egypt, Morocco, central and coastal Algeria, Tunisia, central Libya, Syria, and central and eastern Iran. A case study for Morocco revealed that the potential water deficit, which is already apparent for the current climate, becomes even larger for the future climate.